Electrochemical cells and electrolyte reactions have been used extensively to detect particular gases such as oxygen, carbon monoxide, carbon dioxide, etc. Typically, these cells comprise an anode, a cathode, in electrical contact with one another having an electrolyte dispersed between and in contact with each of the electrodes. The cell responds to an object gas which comes in contact with one of the electrodes at the interface of a catalytic surface of the electrode and the electrolyte. The object gas is either oxidized or reduced resulting in the production of electrons. These electrons are then conducted across the catalytic face of the electrode to a collector plate where they are then carried by means of a wire across to the second electrode. The resulting current flow is a measure of the amount of object gas present in the sample.
The electrodes used in the traditional electrochemical gas detection cells are comprised of a hydrophobic, electrically nonconductive support with an electrically conductive, catalytic face in contact with the electrolyte. As the object gas is introduced into the detector, it passes through the porous electrode substrate of the sensing electrode and eventually contacts the catalytic/electrolyte interface. At this interface the object gas undergoes an oxidation/reduction reaction which produces electrons and ions. The electrons are then collected from the sensing electrode (anode or cathode) and conducted through an electrically conductive wire to the counter electrode where a second and opposite reaction takes place. The measure of the current flow between these electrodes is representative of the amount of the detectable gas in the object gas.
These conventional electrode designs produce a number of disadvantages. First, the electrodes have an electrically, nonconductive, hydrophobic substrate. This requires that the conduction of electrons resulting from the catalytic reaction, be collected from the catalytic surface of the sensing electrode. This requires the placement of a collector plate or grid on the catalytic surface of the electrode and in electrical contact with the catalyst surface. In such a configuration, these collector plates or grids are in constant contact with the electrolyte, which is typically highly corrosive. Therefore, these collector plates must be made from corrosive resistant materials, in many instances these materials are exotic and expensive such as tantalum, platinum and gold, adding considerable cost to the entire unit. Additionally, since these collector plates are small, all of the electrons produced at the surface of the electrode must be conducted to it. Therefore, the entire catalytic surface of the electrode must form an electrically conductive continuum. This is only achieved by placing sufficient catalyst material on the surface of the electrode to ensure point to point contact of the catalytic particles. This may require the application of excess catalytic material over the surface to form an effective electrode, just to make sure that the electrical continuity is achieved. Again, this adds additional cost to these detector units.
Yet another disadvantage to these electrodes, is that since the collector plates are placed on the catalytic surface/electrolyte interface, the wires used in conducting the current generated at one electrode to the second electrode, requires that the wires enter and exit the electrolyte cavity. This means that the electrolyte cavity cannot be completely sealed and that there is always a possibility of leakage of the electrolyte at the entrance and exit points of these wires. This leakage, of course, would be disasterous to the operation of the detector.
For these reasons, a new approach is required for designing electrodes specifically for these gas detector units. What is needed is an electrode which does not require electrical continuity across its catalytic face, so that the electrical current can be removed without having the collector plates or electrical wires inside the electrolyte cavity. This would allow designers of these detector units greater flexibility, and potentially produce a gas detector at a lower cost.